Renewable fuse



July 10, 1951 K w SWAIN 2,560,138

RENEWABLE FUSE Filed Jan. 29, 1948 Zyl v 22 20 *H13/g a je 1516 Patented July 10, 419511 RENEWABLE FUSE Kenneth W. Swain, Hampton, N. H., assignor to The Chase-Shawmut Company, Newburyport, Mass., a corporation of Massachusetts Application January 29, 1948, Serial No. 5,091

12 Claims.

This invention relates to improvements in renewable fuses of the knife blade cartridge type. More particularly it provides improvements whereby substantial savings may be effected in the costs of manufacture and initial assembly of such fuses and which facilitate the removal therefrom of blown or otherwise defective fuse links and substitution therein of new links. Also, the improved structure results in fuses which operate several degrees cooler than the available comparable fuses of the same rated capacity under similar service conditions, and which provide Alonger time delay on moderate overload.

It is among the objects of the invention to provide renewable cartridge fuses of the blade-terminal type wherein the removable link-carrying unit comprises a minimum of parts which quickly may be assembled into a rigid unit on which a fuse link may be mounted without disturbing the rigidity of the unit.

Another object is to provide renewable knife blade cartridge fuses having a removable linkcarrying unit comprising a minimum number of parts and having its opposite end portions identical.

A further object is to provide a renewable knife blade cartridge fuse whose removable link-carrying unit is identical in structure at each end and is insertiblein its casing with either end of the unit constituting the leading' end when the unit is being inserted through an end of the casmg.

Yet another object is to provide a renewable knife blade cartridge fuse whose removable linkcarrying unit has a relatively massive heat-conducting member loosely mounted on each end portion of the unit for self-adjusting clamping coaction with end elements of the fuse casing.

Still another object is to provide a renewable knife blade fuse wherein relatively massive heatconducting members coact with end elements of the fuse casing to close the opposite ends of the casing and wherein vent passages having substantial surface areas for cooling extend directly through the said massive members to atmosphere.

A yet further object is to provide a renewable knife blade fuse wherein relatively massive heatabsorbing members are mounted on the knife blade elements at opposite ends of the fuse casing and coact with end elements of the casing to close the opposite ends thereof, each said heat-absorbing member being adapted to quickly absorb considerable amounts of heat incident to a fusing of a fusible element of the fuse, and each having vent passages leading directly through it to atmosphere, with substantial areas of vent passage walls for cooling the venting gases.

Another object is to provide a renewable knife blade fuse having a minimum number of parts which may be readily and economically assembled to produce a fuse having superior time delay and low-temperature operating characteristics.

It is, moreover, my purpose and object generally to improve the structure and operation of knife blade cartridge fuses and especially such fuses of the renewable type.

In the accompanying drawing:

Fig. 1 is a side elevation of a renewable knife blade fuse embodying features of the invention, the casing elements being in medial cross-section;

Fig. 2 is a cross-sectional view on line 2 2 of Fig. l;

Fig. 3 is an end elevation of the fuse of Figs. 1 and 2;

Fig. 4 is an exploded perspective view of the removable link-carrying unit of the fuse of Figs. l and 2; and

Fig. 5 is a side elevation of the assembled linkcarrying unit, with the fuse link shown in separated relation.

Referring tothe drawing, the tubular casing member lil may be made of vulcanized fibre or other suitable insulating material, each end portion of the tube being interiorly threaded at l2 for receiving one of the exteriorly threaded metal ferrules I4, I6, one ferrule being screwed into one end of the tube and one into the other end, and both being permanently secured against removal from the tube as by having the metal deformed outwardly at I3 into the tube walls at one or more locations around the walls.

At least one of the ferrules l ll, i6, herein shown as the ferrule I, is in the form of a sleeve which has substantial projection out of the insulating tube and whose projecting portion is provided exteriorly with the screw threads 253 which are substantially larger than the threads within the tube, so that an end cap 22, with relatively large diameter central opening 24 therethrough, may be screwed on the ferrule I4. Both end ferrules may be the same, with an end cap screwed thereon, but I prefer to form the end cap 26 integral with ferrule I6 so that it becomes permanently xed on the end of the tube when the ferrule I6 is secured. However, the end cap 26 has a relatively large diameter central opening 28 therethrough similar to that in end cap 22 and the outward appearance of the two end caps on the tube is substantially the same.

The removable unit of the fuse assembly comprises two similar terminal blades 30, each having its inner portion 32 reduced in width to provide the oppositely disposed inwardly facing shoulders Bil. A relatively massive disk @it is mounted on the reduced portion 32 of each blade 3G, each disk having a slot 38 therethrough for slidably receiving the portion 32 of a blade, so that the disk may be slipped` on. the portion 32 and be seated against the shoulders 3Q.

A rectangular recess llt is formed in the inner face of each disk 35, along one side of the reducedportion S2 of a blade 3G, with said portion 32 constituting one wall of the recess, and. a stiff:

bar l2 of insulation materialhasits opposite end portions slidably and non-rotatably engagingin said recesses of the oppositely disposedfdisks 3i?, with a flat surface of the bar engaging iiatwise against the reduced portion 31?-- of each blade so that each end portion of bar l2 maybe effectively and securely clamped to the adjacent portion 22 by a single screw 154 passed loosely through a hole @.5 inthe bar and screwed intona threaded hole Q8 in the portion 32, with each screw [it having substantial threaded extent beyond the portion 32.

.in assembling these parts, starting at one end, one of the disks 36 is slipped on the reduced portion 32of one of the blades 3i), and one end of bar i2 is inserted in recess i in the disk so as to rest flatwise against the reduced portion 32 of the blade, after whichk a screw lil is inserted through hole 4S, in the bar and screwed into threaded hole 48 in blade portion` 32 until the bar i2 and portion 32 are clamped securely together. The other end is assembled in the same manner to provide an extremely strong and rigid unit as shown in Fig. 5, which is ready for yconvenient mounting thereon of the fuse link 5B.

The fuse link 50 may be of any conventional `or special design and is `shown-provided at one end with a customary notch 52 extending longitudinally of the link inward from the link end, whereby this end of the link may be engaged around the threaded projecting portion of one of the screws iid. lThe other end of thelink has a notch 5lextending laterally inwardfrom one side edge, so that this end may be yswung into engagement with its screw 1M, with the rst mentioned screw serving as a pivot. The opposite ends of the link then may be secured in place by` means of the nuts 5t, one being screwed on each screw dll, preferably with a washer 53 and locking spring 50 intervening between the fuse link and the nut on each screw.

t will beapparent from the foregoing description, in connection with the drawing, thatboth ends of the link supporting removable unit are precisely the same, asbest seen in Fig. 5. Also, it will be apparent from an examination of Figs. l and 2 that the disks 36 have exterior diameter less than the interior diameter of the ferrules lll, EG, but only slightly less. Hence, with a. casing as illustrated in Figs. 1 and 2, either end of the removable unit may be inserted first through the end of the casing which is tothe left in the drawing, assuming that end cap 22 has been removed. rIhe unit will be inserted until the leading disk engages the annular vertically disposed portion 2ll of end cap 26, following which the end cap 22 may be screwed on the ferrule lil with its annular vertically disposed portion 23 engaging the adjacent disk `3S. Tightening of cap 22 puts the interior unit under endwise compression between the lannular vertically disposed portions 2l and 23 of the end caps, with the disks d 36 clamped tight against the opposite ends of the bar 42.

It is a feature of importance that each disk 38 has appreciable looseness on the blade portions 32 after the removable unit has been assembled as in Fig. 5, and prior to clamping of the unit within a casing. Actually appreciable clearance is provided between the blade portions 32 and the Walls. of the disk slots 38 and between the end portions of bar @2 and the walls of the disk recesses 4S, excepting that wall of each recess Miwhich is provided by a blade portion 32 and against` which the end portions of the bar l2 are tightly clamped by screws 44. Hence, in Fig. 5, each disk 3 6 caribe tilted slightly as indicated bythe dotted lines in Fig. 5. As a result, when the removable unit is being clamped within a casing, the disks are self-adjusting to an appreciable extent to overcome minor departures from precision dimensioning of parts.

, Referring to this. assembled unit of Fig. 5, and to the exploded represen-tationof its elements as represented in Fig. 4, it will be apparent that each of the relatively thick disks 35 is slidably mounted on a knife blade but is positively locked against rotation thereon, and that each disk slidably engages over an end of the insulating bar 22, whose endsV extend into the disk recessesv 38. Hence, each end of bar l2 is positively locked by a disk 36 against relative rotation of a-knifeblade and the bar about the axis vof a clamping screw fill. This` function of inter-engagementof the ends of the insulating bar in the recesses ofthe disks to prevent relative rotationbf the blades and the bar about the axes of the screws 436i definitely avoids any mis-alignment of the blades and bar both atthe time of -initial assemblyand' when the fuse, in service, is subjected to stresses whichktend tocause mis-alignment of the blades and the bar, suchas stresses incident to expansion of parts when a fuse has been operating atelevated temperatures. In this .connection, itis important to note thatthedimensions of the knife blades, Vdisks and bars may vary quite appreciably with temperature changes,v

r and the dimensions of the bar i12 in particular may varyk considerably with changes in moisture` content. 'Howeven the variationsof the knife blades and bar primarily affect their lengths, the width dimensions being so, relatively smallthat any width variationsfare inconsequential. Hence,

the width dimensions of the bar, and of the disk recesses, and of the portions 32 of the knife blades, maybe controlled within ratherclose lim: its to be substantiallyl uniform in each fuse -regardless of temperature and moisturegconditions. The bar 152, on the other hand, isassembledwith its ends locatedwithin the disk recesses butshort.

of the bottoms of therrecesses when Ythe disks are againstY the kniferblade shoulderst., so that. variationsin its length are accommodated,within` the recesses. However, during mountingsof .the

inner unit in a fuse casing, each disk slides on,

its knife blade into contact withthe kadjacent end of the bar, they being thus self-adjusting for endwise clamping of the bar regardless `of its length-variations..r However, the describedlocked alignment of` blades and bar is maintainedv blades, while other gases escape between the large-area peripheral surfaces of the disks and the adjacent ferrules and thence between the annular vertically disposed portions 23 and 21 of the end caps and the engaged adjacent marginal portions of the disks, these gases too being cooled to safe discharge temperatures.

It has been mentioned previously herein that my improved cartridge fuses operate several degrees cooler than prior comparable fuses under comparable service conditions. This cooler 0peration no doubt results in part from the more eifective venting both through and around the disks 36. But the relatively massive character of the disks plays an important part in the dissipation of heat generated under conditions of normal loads and moderate overloads. Each disk constitutes a substantial heat-conducting mass which absorbs considerable amounts of heat and which has relatively large surface areas for dissipating heat directly to atmosphere at the large end openings 213 in the caps and indirectly to atmosphere through the end caps and ferrules. Also, the substantial heat-absorbing nature of the disks 36 increases time delay on moderate overloads. On short circuits, and the like, the massive disks 3S act as heat absorbers which substantially reduce the temperature of the hot gases prior to their venting and which condense the molten products of the fusing.

The disks 36 may be made of any good heatconducting material having the required rigidity of mass. I have foundI that powdered copper molded according to known procedures provides excellent heat-absorbing and heat-dissipating disks 36 which may be economically produced with the required accuracy of dimension, and with desired uniformly smooth surfaces. As previously explained, when these disks are mounted on the unit of Fig. 5, their appreciable looseness makes it unnecessary to have that exactness of precision dimensioning of the casing parts and of the insulating bar which otherwise would be i essential.

I claim as my invention:

1. In a knife blade cartridge fuse having a tubular casing, a unit insertible in and removable from the casing, comprising a pair of knife blade terminals, means for mounting a fusible element in electrical connection with said terminals, a relatively thick circular mass of heatconducting material slidably and non-rotatably mounted on each said terminal, abutment means on each said terminal limiting movement of a said mass in outward direction along the terminal, a stiif bar of insulating material rigidly inter-connecting said terminals, each end of said bar having angular cross-section, walls dening an angular recess in each said mass in one of which recesses each angular end of said bar is engaged limiting movement of said masses in directions inward along said terminals and positively locking said circular masses and the bar against relative rotation., said circular masses of heat-conducting material each having appreciable looseness on its terminal and between the said limiting abutment on the terminal and the adjacent end of said bar whereby said masses can be tilted slightly in diierent directions on their terminals, and substantial venting passages leading between relatively large-area cooling surfaces of the masses and terminals directly through said masses, and means on the opposite ends of the said casing for engaging only annular marginal portions of saidv circular masses for 6 clamping them against the opposite ends of said stiff bar.

2. In a renewable knife blade cartridge fuse, a fuse link mounting unit comprising a pair of knife blade terminals, means for mounting a fuse link on the unit in electrical connection with said terminals, ,a relatively massive disk slidably mounted on each terminal, each said disk having a slot therethrough whereby it may be slipped on a terminal with appreciable looseness between the terminal and the walls of the slot, a relatively stiff insulating bar extending between and secured to the inner end portions of said terminals inward of said massive disks on the terminals, each end portion of the bar having angular crosssection, and each said disk having an angular recess in its inner face for engaging with `appreciable looseness over the adjacent angular end of said bar for positively locking the disks and bar against any substantial relative rotation, and means on each said terminal outward of the disk thereon restricting outward movement ofthe disk and providing for only limited movement of the disks between said restricting means and the ends of said bar, whereby said disks are self-adjusting when said unit is mounted in a fuse casing with said slots in the disk providing ventingpassages leading directly through the disks between the slot walls and the adjacent surfaces of the terminals.

3. In a renewable knife blade cartridge fuse having a tubular insulating casing, a fuse link mounting unit insertible in and removable from the casing, comprising a pair of knife blade terv minals, each having `an inner end portion of reduced width whereby inwardly facing edge shoulders are provided on each terminal, means for mounting a fuse link on said unit in electrical connection Iwith said inner end portions of the terminals, a massive slotted disk slidably mounted on the reduced portion of each terminal and having appreciable looseness thereon, each said disk having an angular recess in its inner face, a stiff insulating bar extending between said terminals and secured to the inner end portions thereof with each end of the bar angular in cross-section and engaged in a said disk recess whereby the disks and bar are positively locked against relative rotation, and means on the opposite ends of said insulating casing for clamping said disks against the ends of said bar with the disks selfadjusting on said terminals in response to the clamping pressure and with said appreciable looseness of the disks on the terminals providing venting passages leading directly through said disks to atmosphere.

4. In a knife blade fuse having a tubular cas-l ing, a unit insertible and removable through an end of the casing comprising a knife blade terminal at each end of the unit, means for mounting a fusible element on said unit in electrical connection with said terminals, a relatively stiff insulating member extending between the terminals and secured to the inner end portions thereof for maintaining them in predetermined spaced relation and against relative rotation, a generally circular body slidably mounted on each terminal and having generally parallel outer and inner faces, abutment means on each terminal limiting outward movement of a said body along a said terminal, each said body having a recess in its inner face, and said insulating member having its end portions slidably and non-rotatably engaged in said recesses and constituting the only meanslimiting inward movement of said.

bodies along said terminalsandf positively locking said bodies and said insulating member against; relative rotation, and annular means on eachendof'said casing for engaging the margin of the outer face of a said" body, said annular meansat atleast one endlof the casing being operable to1 effect a clamping of said bodies against-theAends-of saidf insulating member, withl saidannularmeans andv said bodies coacting to close' the opposite ends of? said tubular casing.

51 In a kniferv blade fuse having al casing and havinga pair ofknife bladel terminals projecting out'v of the casing atv` the. opposite ends thereof eachy of said terminals having abutment means thereonl between its ends, means for mounting a fuse linkin electricaly connection'withsa-idY terminals; aslottedy disk' mounted loosely on the inner endl portion of each terminal with saidl abutmentl means limiting outward movement of the disks along the terminals, an insulating memberconnected to andextending between the innerl end portions of saidterminals, the opposite ends of said insulating. member being in the pathl of-v inward movements ofsaid disks `and constitutingy the only means limiting inward movements of: said disks along said terminals, and means onsaid casing for electing movements of said disks relativefto said terminals into clamping engagement with. the opposite ends of-said insulating member.

6l'. In arknife blade fuse having a tubular insulating casing, a unit insertible in and removable fromthe casing comprising a pair of knife blade terminals'each having abutment means thereon between its ends, means for mounting afuse link on said* unitr in electrical connection with the terminals, aslotted disk loosely arranged on the innerv end portion of each terminal with said abutment means on the terminals limiting outward movement ofV thefdisks along the terminals, the twosaid disks being identical, an insulating member connected to and extending between the inner end portions-of said terminals, each endv of the insulating member constituting an abutment between *which and a said terminal abutment means each said slotted disk can move appreciably in directions-along itsk terminal, said disks having dimensions whereby either end of saidv unit may be inserted through an end of said casing, .and annular means on each end of the casing for engaging outer portions of said disks to draw them relatively toward each other with said disks moving relative to their respective terminals into clampingengagement with the opposteends of said insulating member and with said terminals extending through the slots inthe disks with appreciable clearance.

7. In a knife blade fusev having a tubular insu-A lating casing, a-unitLinsertible in and removablefrom the casing comprising a pair of knife blade terminals each having abutment means thereonV between its ends, means for mounting afuse link on said unit in electrical connection with the ter'- minals, a slotted disk loosely arranged on the inner: end portion of each terminal with said abutment means-on the terminals limiting out- Ward movement of 'the disksalong theterminals,

an insulating bar.' connected to and extending between the inner end portions of said terminals, there being a recess in the inner' face ofr each said: disk' and theend portions of said bar being slidablyl and lnon-rotatably engaged insaid recesses'of the disksrlimiting outward movement of' the disks along the terminals and positively locking4 the.- disks andbar against-- relative-rotation;

annular' abutmentv means on one endv ofsaid'- cas'- ingvi for' engaging the' margini of the7 outer face of one of' said disks, and removable annular meansv on the otherend of' the casingA for engaging thei margin ofthe outer face-of the'other one of sa-id disks, said removable annular mea-nsbeing operable along the casing to urge said disks-rela'- tively toward each other with the saidA insulating bar constitutingtheL sole means limiting their relativeY movement toward each other.

8". In a knife bladefusehaving a tubularinsulating casing, a f-use link mounting unit insertible in` andy removable fromy the casing and having its opposite ends substantially identical so that either end of" theunit may be insertedy rst' through an end of the-casing, said unit comprising'apair of knife blade terminals, an insulating bar connected to and extending between the inner endl portions of the'terminals, and a relatively thick andV massive disk on each terminal, each said disk having a slot therethrough for passage of a said terminal through the disk', and each having a recess in' its-inner face' for reception of" an end portion of said insulating bar, the walls of' said recesses and the end portions of said bar' coacting to positively lock the said disks and bar against relative rotation, and means on the ends of said casing for engaging and clampingV said' disks againstv theopposite` ends of said insulating. bar.

9. In a fuse having a tubular casing and a terminal projecting generally axially at' each end' of the casing, means for mounting a fuse'link in electrical connection with the said terminals, means at each end' of the casing for closing the ends of the casing around the terminals and for providing uniform ventingpassages between relatively large-area heat-absorbing' surfaces, said means at each' end ofl the casing comprising a thick disk having a smooth peripheral surface of relatively large area fitting within said casing with a predetermined precise clearance whereby a relatively longannular vent passage is provided along the peripheral surface of the disk, each said disk having a slot therein through which. a

said terminal extends with appreciable clearance whereby venting cracks extend. directly through the'disks, abutment means on eachterminal limitingY outward movements of the disks along the terminals,` an insulating bar connecting the inner ends of the terminals and having its opposite ends constituting the only means limiting in*- ward movements of the disks along the terminals, and an annular depending flange on the' casing engaging only a narrow` marginal. area of each said disk at one end of a said. annular vent passage whereby pressure gases can escape' from said passage between said flange and the engaged margin of the disk and also directly through. the disks at said venting cracks.

10; In a knife blade cartridgel fuse' having' a tubular casing, a unit insertible in and removable from the casing, comprising a pair of knife blade terminals, each having inwardly facing abutment means thereon, means for mounting a fuse link on the inner end portions'of the terminals, a stiff bar of insulating material extending between and'connected to the4 inner end'portions of-"said terminals, each end of the bar being spaced substantially inward from said abutment means on the terminal tov which'it is connected, a relatively massive heat-absorbing member slidably and non-rotatably mounted on each. terminal between said abutment` means on the terminal" and' the adjacent' end'l of said; insulating bar, said adjacent end of the insulating bar constituting the only means limiting inward movement of the heat-absorbing member along the terminal, whereby said heat-absorbing members are self-adjusting on their respective terminals for accommodating dimensional variations in the associated parts, said heat-absorbing members having diameter less than the internal diameter of the casing whereby either end of the insertible unit may be the leading end when inserting the unit in its casing, and means on the opposite ends of the casing for coacting with said heat-absorbing members to close the opposite ends of the casing with said heat-absorbing members presenting relatively large heat-absorbing surface areas in positions to be directly contacted by the hot gaseous products of a fusing within the casing.

11. In a knife blade cartridge fuse having a tubular casing, a unit insertible in and removable from the casing, comprising a pair of knife blade terminals, means for securing a fuse link on the inner ends of the terminals, a generally circular solid mass slidably and non-rotatably mounted on each said terminal, means on each said terminal limiting movement of a said mass in direction toward the outer end of the terminal on which it is mounted, each said mass having a recess therein. a bar of insulating material extending between said terminals and having its opposite ends engaged in said recesses of the solid masses. means securing said bar to each said terminal at locations spaced inward from the said engaged ends of the bar, said securing means and said recess walls of the solid masses coacting to maintain the terminals and the bar approximately in a predetermined alignment.

l0 12. In a knife blade cartridge fuse having a tubular casing, a unit insertible in and removable from the casing, comprising a pair of knife blade terminals, means for securing a fuse link on the inner ends of the terminals, a generally circular solid mass slidably and non-rotatably mounted on each said terminal, a stiff bar of insulating material extending between said terminals, means inward from each end of said bar for securing the bar to the respective terminals, each said solid mass on the terminals having a recess therein, and each end of said bar being slidably engaged in a said recess, whereby the walls of said recesses positively lock the said terminal and bar againt relative rotation about said securing means.

KENNETH W. SWAIN.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,861,744 Johnson June 7, 1932 1,874,948 Fogal Aug. 30, 1932 1,919,273 Conant July 25, 1933 1,928,997 Kirkman Oct. 3, 1933 1,991,876 Wood Feb. 19, 1935 2,036,177 La Mar Mar. 31, 1936 2,195,147 Griiiith Mar. 26, 1940 2,198,663 Floten Apr. 30, 1940 2,280,565 Wood Apr. 21, 1942 2,293,953 Taylor Aug. 25, 1942 

